Kinetics of hydrolysis of BCNU was studied at constant ionic strength and temperature over the pH range of 2.0 to understand the mechanism of hydrolysis of halogenated nitrosoureas. The results show that proton at N3 is definitely involved in increasing the rate as the pH is increased from 4.0 to 9.0. However, previously published reports attributing the ionization of N3 - proton as the major factor increasing the rate near neutral pH's does not appear to be consistent with the kinetic data obtained, and also from attempted pKa determination by potentiometric titration. Further work to explain the observed kinetic data is in progress.